1. Field of the Invention
The present invention relates to an ink jet head that records by discharging ink droplets from the discharge openings to a recording medium. The invention also relates to an ink jet apparatus which is provided with such ink jet head.
2. Related Background Art
For the execution of ink jet recording, ink is discharged and impacted on a recording medium for recording. However, the ink jet recording presents a phenomenon that ink may splash about at the time of impact.
Now, with reference to FIGS. 2A to 2C and FIGS. 3A to 3C, the description will be made of the ink splash phenomenon at the time of impact.
FIG. 2A shows a head 10, a discharged droplet 12, and a recording medium 11. FIG. 2B shows the state of the droplet being impacted. FIG. 2C shows the state that the rebounded mist 14 (hereinafter also referred to simply as mist) takes place at an acute angle to the recording medium. Here, a reference numeral 13 designates an impacted ink droplet. FIGS. 3A to 3C are views which illustrate the state that a plurality of droplets are impacted on one dot formed on a recording medium. FIG. 3C shows the state that the rebounded mist 14 occurs more conspicuously at the time of impact if there is an ink droplet 15 that has been formed on the recording medium (immediately) before the current impact. Here, a reference numeral 16 designates the ink droplet which is impacted anew for the current event.
The mist thus generated at the time of impact is caused to adhere to the facing area of the ink jet head where the discharge openings are formed. This mist adhesion may result in the deviated impact or disabled discharge.
Also, an ink jet apparatus that prints color images is structured to arrange each of the ink jet heads on the same scanning line for discharging each ink of the fundamental colors. Then, during scanning performed by these ink jet heads, discharge signals are delayed for a period of time corresponding to the respective the distances between each of them so that a plurality of ink droplets, which are discharged from different ink jet heads, are overlaid on one and the same location, thus forming dots of halftone colors from the fundamental colors. For an ink jet apparatus of the kind, the generation of mist as described above is particularly conspicuous.
Therefore, it is arranged for an ink jet head of the kind to apply water-repellent agent to the facing area of the head where the discharge openings are formed so as to repel the ink droplets near the discharge openings for the prevention of any possible discharges that may be disabled or twisted.
Also, for the conventional ink jet apparatus, the facing surface is wiped or cleaned off at certain time intervals to remove the ink droplets deposited on the facing surface, thus coping with the unfavorable aspect of the operation as described above.
Also, for the ink jet recording, there is a method for using liquid that reacts upon ink (hereinafter referred to as water proof liquid) in order to provide water proof capability to the printed object.
More specifically, the water proof liquid is discharged from the ink jet head to mix it with ink on a printing medium so that the intended reaction may take place on the printing medium for the provision of the water proof capability. In other words, as in the same manner as the color ink jet recording, the water proof liquid and ink are overlaid when impacted on the printing medium.
However, for the conventional ink jet apparatus, there is such a problem as to cause the water-repellent agent formed on the head surface to be worn out when the head surface is wiped or cleaned off. Also, there is a problem that the facing area of the head is worn away by such wiping and cleaning, thus making the life of the head shorter.
Also, for the ink jet recording that uses the water proof liquid, there are some cases where firmly solidified and fixing substances may adhere to the facing area of the head due to the reaction between the water proof liquid and ink, which have splashed about the time of impact. Then, a problem is encountered that some dots may be missing in the printed images as a result of the deviated impacts or the phenomenon that ink is not discharged from the printing head in some cases.